Stripline directional coupling device

ABSTRACT

A segment of a main transmission line is located equidistant between and parallel to a first and second coupling segment. The first coupling segment has an input terminal at one end thereof for connection to a stub line. The second coupling element has a terminating impedance located at the end thereof opposite said input terminal end of said first coupling segment. A conductor connects the other opposite ends of said first and second coupling segments so that a pulse travelling thru said main line segment or said first coupling segment in a direction away from said input terminal end of said first coupling segment will couple to the other travelling in the reverse direction.

United States Patent [72] Inventors Murray H. Bolt Raleigh, N.C.; Howardll. Nick, Potomac, Md.; Edward C. Uberbacher, Poughkeepsie, NY. [21]Appl. No 887,964 [22] Filed Dec. 24, 1969 [45] Patented Aug. 24, I971[73] Assignee International Business Machines Corporation Armonk, N.Y.

[54] STRIPLINE DIRECTIONAL COUPLING DEVICE 11 Claims, 5 Drawing Figs.

[52] US. Cl 333/10, 333/84 M [51] Int. CL l-l0lp3/08,

HOlp 5/14 [50] Field of Search 333/10, 6,

[56] References Cited UNITED STATES PATENTS 3,278,864 10/1966 Butler333/10 3,516,024 6/1970 Lange 333/10 Primary ExaminerHerman KarlSaalbach Assistant Examiner-Marvin Nussbaum Anorneysl'lanifin and Jancinand Harold H. Sweeney, Jr.

ABSTRACT: A segment of a main transmission line is located equidistantbetween and parallel to a first and second coupling segment. The firstcoupling segment has an input terminal at one end thereof for connectionto a stub line. The second coupling element has a terminating impedancelocated at the end thereof opposite said input terminal end of saidfirst coupling segment. A conductor connects the other opposite ends ofsaid first and second coupling segments so that a pulse travelling thrusaid main line segment or said first coupling segment in a directionaway from said input terminal end of said first coupling segment willcouple to the other travelling in the reverse direction. Y

STRIPLINE DIRECTIONAL COUPLING DEVICE This invention relates todirectional couplers and more particularly, to an improved striplinedirectional coupling device.

With the increase in operating speed of devices, such as computers, intothe nanosecond range, it has been found that directional couplers can beutilized to couple these high-speed pulses to and from transmissionlines with respect to stub lines leading to and from various peripheraldevices. In copending U.S. application, Ser. No. 609,083, filed Jan. 13,1967, and now U.S. Pat. No. 3,516,065, issued June 2, 1970, a system fortransmitting digital data between a plurality of data-processing devicesusing stripline directional couplers is disclosed. The use of thedirectional coupler in this system eliminates the stub lengthlimitations and allows any stub or stub lines connecting individualdevices to the transmission line to be limited in length only by thedegradation of a signal passed along the line.

As is known, a stripline directional coupler is a device wherein twoparallel adjacent printed circuit striplines sandwiched between twoground planes are inductively and capacitively coupled so that the edgesof a first pulse, of fast rise and fall time characteristics,propagating along one line, produces a positive pulse and a negativepulse in the other line. The lines are back coupled or directional inthat the thus produced pulses propagate along the second line in adirection opposite to the direction in which the first pulse propagatesalong the first line. The energy transferred between the couplingsegments of the two-element directional coupler is affected by thevarious physical characteristics of the directional coupler such as thelength, width and distance between the coupling segments. Accordingly,the long coupling element lengths needed to obtain a good energytransfer between the segments of the coupler introduces obviousdisadvantages in packaging the two-element directional coupler,especially where a large number of such devices are to be combined inthe same package.

It is an object of the present invention to provide a directionalcoupler which provides a higher energy transfer than the prior artdirectional couplers.

It is another object of the present invention to provide a striplinedirectional coupler which provides a higher voltage magnitude couplingwith shorter coupling segments.

It is a further object of the present invention to provide a striplinedirectional coupler in which a pulse passing through the main segment issubject to a shorter or smaller through put delay.

It is another object of the present invention to provide a I striplinedirectional coupler which can be packaged in a much smaller space.

Briefly, a directional coupler is provided for coupling to and from amain line conductor. The coupler comprises a segment of a maintransmission line conductor which is located equidistant between andparallel to a first and second coupling segment. The first couplingsegment is part of a stub line conductor connecting the maintransmission line to peripheral devices. The second coupling element hasa terminating resistance located at the end thereof opposite said end ofsaid first coupling segment connected to said stub line. A connectingconductor is .connected between the other opposite ends of the first andsecond coupling segments so that a pulse travelling in a given directionalong said main transmission line or said stub line will couple in theopposite travelling direction to said stub line or main transmissionline, respectively.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of a preferred embodiment of the invention as illustrated inthe accompanying drawings.

FIG. 1 is a schematic diagram of the prior art two-element directionalcoupler showing the input and output waveforms thereof.

FIG. 2 is a schematic diagram of the three-element directional couplershowing the input and output waveforms thereof.

FIG. 3 is a schematic diagram showing the three-element directionalcoupler connected in a full duplex scheme.

FIG. 4 is a schematic diagram of the three-element directional couplerconnected in a full multiplex system.

FIG. 5 is a schematic diagram of the three-element directional couplerconnected in a directional multiplex system. I

Referring to FIG. 1, there is shown a schematic diagram of the prior arttwo-element directional coupler which consists of two conductivesegments 10 and 12 extending parallel to one another from an end A to anend 8. Usually, the conductors are mounted on a substrate 14 made of anonconductive material such as epoxy glass and are arranged between twoground planes 16 and 18 which usually consist of sheets of copperarranged over and under the conductors. Each conductive element 10 and12 has a terminal 20, 22 at the end B of the coupler serving as an inputor output terminal. Each conductor 10, 12 has a terminating resistance24, 26 connected at the A end of the coupler which matches the couplerto the characteristic impedance of the lines to which it is connected.The coupling takes place along the length of the segments 10, 12. Thecoupler operation depends upon the steepness of the incident pulse riseand falltime. The width or duration of the pulse produced by thecoupling is determined by the lengths L of the two segments 10, 12 inparallel. The performance of the coupler is related to the impedancesoffered to signals on the transmission lines and the coupling ratio,which are determined by the widths of the lines in the coupled region,the thickness of the lines, the distance between ground planes, and therelative dielectric constant of the material. It has been determinedthat coupling segments of electrical length L will produce a pulsehaving a time duration equal to 2 L. For example, a l-volt amplitudeinput signal applied to the input terminal 20 of segment 10 when thecoupler has a coupling ratio of l to 4 and an electrical length L of2nsec, will produce an output pulse having a time duration of 4nsec anda pulse amplitude of V4 volt. The input pulse can be generated by adriver connected to the coupler by a stub transmission line. As shown inFIG. 1 by arrows, the coupled pulse travels in an opposite direction inthe main line segment 12 to the direction of travel in the couplingsegment 10. It will be appreciated, that a pulse travelling from B to Aalong the main transmission line 12 will likewise be coupled to thecoupling segment 10 in the opposite direction. A stripline coupler isoperated by the edge of the wave passing along one of the lines and thiswave edge should have a rise or falltime that is twice as fast as thetime duration of the pulse induced in the coupling in order that therelationship of the height of the induced pulse be related to the heightof the driving pulse in the manner defined by the coupling ratio.

A three-element directional coupler, forming the present invention, isshown schematically in FIG. 2. The middle segment 28 corresponds to themain line segment 12 of the prior art directional coupler of FIG. 1. Thecoupling segment 30, having a-terminal 32 at the right hand or B end,corresponds to the coupling segment 10 as shown in FIG. 1. In additionto the arrangement as shown in FIG. 1, a further coupling segment 34extends parallel to and spaced from the other side of the main linesegment 28. The spacing of the further coupling segment 34 from the mainline segment 28 is the same as the spacing S between the input couplingline segment 30 and the main line segment 28. This further couplingsegment 34 is of the same width as the input coupling segment 30. Theinput couplingsegment 30 and the further coupling segment 34 each havean opposite end thereof connected together by a stub connector 36. Thus,the input coupling segment 30 has the left end A connected to the rightend B of the further coupling segment 34. The left end A of the furthercoupling segment 34 is'terminated in a terminating resistance 38 of avalue equivalent to the characteristic impedance of the line in whichthe segment is connected. s shown, one end of terminating resistor 38 isconnected to ground by a ground connection 40. The A end of the maintransmission line 28 is likewise terminated in an impedance 42 havingthe same characteristic impedance as the line.

As was previously mentioned in connection with FIG. 1, the directionalcoupler segments are stripline-type conductors which are well known inthe art. These conductors are usually closely packed and can best bemanufactured by utilizing one of the well known masking and etchingtechniques used extensively inthe manufacture of printed circuits. It isnecessary to have the appropriate ground planes for operation of thedirectional coupler. These can consist of thin sheets of copper 46arranged both below and above the conductors. The segments 28, 30, 34are located on the polyglass base 44 which serves as a dielectric toelectrically isolate the segments from the below located ground plane46.-Of course, a dielectric sheet can be included between the upperground plane and the segments for electrical isolation. If the schematicarrangement shown in FIG. 2 has 8 mil wide segments separated from oneanother by 6 mil spacings S, and the segment length L is approximately 2nanoseconds in electrical length or approximately 11 inches inpolyglass, and the epoxy glass stripline package is approximately inchesthick, a l to 4 coupling ratio results. The two-element prior artdirectional coupler shown in FIG. 1 also has a 1 to 4 coupling ratio anda segment electrical length of 2 nanoseconds. With a 1 to 4 couplingratio, an input pulse of l-volt amplitude applied at the input terminal32 of the input coupling segment 30 provides an output pulse on the mainline conductor 28 as indicated in FIG. 2.

' It should be observed that the l-volt amplitude pulse applied to theinput terminal 32 of the coupling segment 30 is the same as the pulseapplied to the coupling segment of the priorart in FIG. 1. It shouldalso be noted that the resulting output pulses are quite different. InFIG. 2, it can be seen that theoutput pulse has a 6 nanosecond durationand is half a volt high in the center 2-nanosecond portion thereof.Thus, a three-element directional 'couplerhaving the same coupling ratioand segment electrical length as a two-element prior art directionalcoupler is capable of producing a coupled output pulse having a greaterduration and a greater voltage amplitude.

Acomparison of the energy content between the two output pulses showsthat the energy content of the two-element coupler output pulse of FIG.1 equals 0.278 ergs while the energy content of the tri-coupler outputpulse of FIG. 2 equals 0.834 ergs. The percentage increase in energycontent between the two-element and the tri-coupler directional couplerequals 200 percent. The two-element directional coupler has an averagevoltage height of 0.167 volts over a 6 nanosecond time period while theaverage voltage height of the tri-coupler output pulse is 0.333 voltsover a 6 nanosecond time period. The percentage increase in averagevoltage height for an equivalent time period between the two-element andthe tri coupler directional coupler is 100 percent. The three-segmentcoupler or tri-coupler may be packaged in 40 percent less space than theequivalent two-element coupler. Because of the greater energy andvoltage amplitudes obtained through the use of the tri-couplerarrangement, greater loads may be driven over longer lengths of cablethan is possible in the equivalent twoelement coupler. It will beappreciated that an equivalent energy pulse output from the tri-couplerrequires less coupling length of segments than is required in the prior',art two-element coupler. Thus, the tri-coupler can be packaged in amuch smaller unit. Also, because of less line length required in thecoupling region to roduce an equivalent" output pulse as compared to thetwo-element coupler, less time is required for a pulse to pass throughthe main segment of the tri-coupler. This can be an important featurewhen a number of tri-couplers are connected to the main line.

A schematic arrangement of a full duplex system using tricouplerdirectional couplers is shown in FIG. 3. The arrangement consists of twotri-couplers, one on each of the cards 50 and 52. A driver circuit 54 isshown connected to one end of the coupled segment 30 and a terminatingresistance 38 is placed at the opposite end of the other coupledsegment. The other ends of the two coupling segments are then joinedtogether by a conductor. This arrangement is now further modified byplacing a receiver circuit 56 at the left end of the main line segmentwith a terminating resistor 42 as shown on card 50. The arrangement asshown on card 52 of'FIG. 3 is a mirror image of the arrangement shown oncard 50. If the open end of each main line segment 28 is joined as isshown between cards 50 and 52, a full duplex system is provided. In sucha system, both drivers may simultaneously produce a voltage ramp which,upon traversing the coupled region, will produce a pulse coupled to thenow joined main segment 28. These two pulses will travel simultaneouslytowards the opposite tri-coupler receivers 56. Thus, the pulse coupledto the main line segment 28 on card 50 derived from its own driver 54will travel toward the receiver 56 on card 52. Likewise, the pulsecoupled to the main line segment 28 derived from driver 54 of card 52will travel towards the receiver 56 of card 50.

FIG. 4 shows a schematic diagram of a plurality of tricouplers connectedso as to provide a full multiplex system. Referring to card 60, a driver62 is connected to one end of one of the coupled elements 30, and aterminating resistor 38 is placed at the opposite end of the othercoupled segment 34; the remaining ends of the two segments are thenjoined together by connecting stub 36. This arrangement is now furthermodified by placing a receiver 64 on one end of the main segment 28. Theother end of the main segment 28 is joined directly to a maintransmission line 66. Card 70 contains a further tri-coupler arrangementwhich is the same as that shown on card 60. Further, tri-couplers may besimilarly connected along the transmission line 66. The main line 66 hasa terminating resistor 72, 74 placed at the left side and right side ofthe tri-couplers, respectively. A third tri-coupler, on card 80, isconnected to the main transmission line 66 with the main line segment 28forming part of the main transmission line. This tri-coupler card islocated at the left of the terminating resistor 72 and has a receiver 82connected to the left end of the main transmission line 66. A pulseprovided at any one of the drivers 62 will latch up each of theotherreceivers 64. For example, a pulse generated by the driver 64 on card 60will produce a pulse on the main segment 28 travelling toward thejunction of the main segment 28 and the main transmission line66. Uponreaching the main transmission line 66, the pulse forms two pulses eachof which then travels in opposite directions along the main transmissionline 66 toward the ends thereof. The pulse which is travelling towardthe tri-coupling coupler as shown on card 70 is sensed by that receiver64 and is latched up. The pulse travelling in the opposite direction issensed by the receiver 82 at the left end of the transmission line 66.Thus, it will be appreciated that each driver pulse applied at any oneof the tri-coupler card drivers 62 will affect each of the otherreceivers 64, 82.

Referring to FIG. 5, a directional multiplex system is shown wherein anumber of tri-coupling devices are connected so that a particularreceiver or receivers will receive information only from a particulardriver or drivers. The main transmission line 84 is shown havingreceivers 86 and 88 at either end and receivers 89, 90, 91 located atdiscrete positions along the length thereof. A number of tri-couplingdevices 92, 93 and 94 are shown each having a driver 95, 96, 97,respectively, at one of the ends of the coupling segment 30 andterminating resistor 38 at the opposite end of the further couplingsegment 34. Connection is made between the opposite ends of bothsegments 30, 34 in each device 92, 93, 94 by a respective connectingstub 36. Noting the orientation of the tri-coupling devices, forexample, tri-coupling devices 93 and 94 are oppositely oriented, it willbe appreciated that the single receiver 86 at the left end of the maintransmission line 84 will receive infonnation from driver 97 of couplingdevice 94 only. Receiver 89 will receive information from driver 97also. The

three receivers 88, 90, 91 at the right end of the transmission line 84and the receiver 89 will receive information from drivers 95 and 96 ofcoupler devices 92 and 93 only. The unique feature here is the fact thatby virtue of its placement along the main line 84, the receiver canreceive information from all drivers on the line or like receivers 86and 88 can be made dependent upon selected drivers for theirinformation.

While the invention has been particularly shown and described withreference to a preferred embodiment thereof, it will be understood bythose skilled in the art that various changes in form and detail may bemade therein without departing from the spirit and scope of theinvention.

What is claimed is:

1. A directional coupling device for coupling electrical pulses to andfrom a main line conductor comprising:

a main line conductor segment having a predetermined length'adapted forconnection at first and second ends thereof to a main line conductor;

a first conductor coupling segment having a predetermined length adaptedfor connection at a first end thereof to a branch conductor, said firstcoupling segment extending parallel to and closely spaced from said mainline segment;

a second conductor coupling segment having a predetermined lengthextending parallel to and closely spaced from said main line segment;

terminating means connected at a second. end of said second couplingsegment for terminating electrical pulses arriving thereat; and

a connecting conductor connecting the second end of said first couplingsegment to the first end of said second coupling segment, so that anelectrical pulse travelling from the first end to said second end ofsaid main line segment will couple to the first and second couplingsegment travelling in the opposite direction and a pulse travelling fromsaid first end to said second end of said first and second couplingsegments will couple to said main line segment travelling in theopposite direction.

2. A directional coupling device according to claim I, wherein said mainline conductor segment and said first and second conductor couplingsegments are sandwiched between first and second ground conductorplanes.

3. A directional coupling device according to claim 2 wherein said mainline conductor segment and said first and second conductor couplingsegments are printed line conductors lying in the same plane. Y

4. A directional coupling device according to claim 3, wherein saidfirst and second conductor coupling segments are equally spaced withincoupling distance from opposite side edges of said main line conductorsegment.

5. A directional coupling device according to claim 4, wherein said mainline conductor segment and said first and second conductor couplingsegments are of the same length,

width, and thickness.

6. A directional coupling device according to claim 1, wherein saidfirst and second conductor coupling segments are spaced withinelectrical coupling distance and equidistant from the main lineconductor segment.

7. A directional coupling device according to claim 1, wherein animpedance matching means is connected to said second end of said mainline conductor segment for matching the impedance of the coupling deviceto the main transmission line to which the coupling device is to beconnected.

8. A directional coupling device according to claim 1, wherein saidterminating means connected to a second end of said second couplingsegment is a resistor having a valve equal to the characteristicimpedance of the branch line to which said coupling device is to beconnected.

9. A directional coupler according to claim 1, wherein a seconddirectional coupler is provided, said main line conductor connecting thefirst end of said main line conductor segment to the first end of saidmain line conductor segment of said second directional coupler so thatan electric signal applied at the first ends of said first couplingsegments of said first and second directional couplers produces coupledelectrical signals on said main conductor line travelling in oppositedirections.

10. A directional coupler according to claim 1, wherein an electricalsignal receiver is connected to the first end of each of said main linesegments and an electrical signal driver is connected to the first endof each of said first coupling segments, a main transmission line havingthe first end of each of said main line segments connected thereto inparallel so that an electric signal applied by said driver to the firstend of each of said first coupling segments couples to said main linesegment travelling .away from said second end of said main line segmenttowards said connection with said main transmission line where saidsignal divides going in opposite directions along said main transmissionline thereby being received by all other of said receivers.

11. A directional coupler according to claim 1, wherein a plurality ofsaid coupling devices are connected at first and second ends of the mainline segments to a common main conductor line, the coupling devices atone end section of said conducting line being mirror images of thecoupling devices at the other end section, receiver means located ateach end of said main conductor line, the coupling devices of both endsections having a pulse applied at the first end of said first couplingsegment so that the pulse couples to said main line segment travellingfrom the second end to the first end along said main line conductorreceives at the other end of said main line conductor, a furtherreceiver means connected to said main. line conductor between said firstand second end sections, said further receiver receiving pulses from thecoupling devices of both end sections.

1. A directional coupling device for coupling electrical pulses to andfrom a main line conductor comprising: a main line conductor segmenthaving a predetermined length adapted for connection at first and secondends thereof to a main line conductor; a first conductor couplingsegment having a predetermined length adapted for connection at a firstend thereof to a branch conductor, said first coupling segment extendingparallel to and closely spaced from said main line segment; a secondconductor coupling segment having a predetermined length extendingparallel to and closely spaced from said main line segment; terminatingmeans connected at a second end of said second coupling segment forterminating electrical pulses arriving thereat; anD a connectingconductor connecting the second end of said first coupling segment tothe first end of said second coupling segment, so that an electricalpulse travelling from the first end to said second end of said main linesegment will couple to the first and second coupling segment travellingin the opposite direction and a pulse travelling from said first end tosaid second end of said first and second coupling segments will coupleto said main line segment travelling in the opposite direction.
 2. Adirectional coupling device according to claim 1, wherein said main lineconductor segment and said first and second conductor coupling segmentsare sandwiched between first and second ground conductor planes.
 3. Adirectional coupling device according to claim 2 wherein said main lineconductor segment and said first and second conductor coupling segmentsare printed line conductors lying in the same plane.
 4. A directionalcoupling device according to claim 3, wherein said first and secondconductor coupling segments are equally spaced within coupling distancefrom opposite side edges of said main line conductor segment.
 5. Adirectional coupling device according to claim 4, wherein said main lineconductor segment and said first and second conductor coupling segmentsare of the same length, width, and thickness.
 6. A directional couplingdevice according to claim 1, wherein said first and second conductorcoupling segments are spaced within electrical coupling distance andequidistant from the main line conductor segment.
 7. A directionalcoupling device according to claim 1, wherein an impedance matchingmeans is connected to said second end of said main line conductorsegment for matching the impedance of the coupling device to the maintransmission line to which the coupling device is to be connected.
 8. Adirectional coupling device according to claim 1, wherein saidterminating means connected to a second end of said second couplingsegment is a resistor having a valve equal to the characteristicimpedance of the branch line to which said coupling device is to beconnected.
 9. A directional coupler according to claim 1, wherein asecond directional coupler is provided, said main line conductorconnecting the first end of said main line conductor segment to thefirst end of said main line conductor segment of said second directionalcoupler so that an electric signal applied at the first ends of saidfirst coupling segments of said first and second directional couplersproduces coupled electrical signals on said main conductor linetravelling in opposite directions.
 10. A directional coupler accordingto claim 1, wherein an electrical signal receiver is connected to thefirst end of each of said main line segments and an electrical signaldriver is connected to the first end of each of said first couplingsegments, a main transmission line having the first end of each of saidmain line segments connected thereto in parallel so that an electricsignal applied by said driver to the first end of each of said firstcoupling segments couples to said main line segment travelling away fromsaid second end of said main line segment towards said connection withsaid main transmission line where said signal divides going in oppositedirections along said main transmission line thereby being received byall other of said receivers.
 11. A directional coupler according toclaim 1, wherein a plurality of said coupling devices are connected atfirst and second ends of the main line segments to a common mainconductor line, the coupling devices at one end section of saidconducting line being mirror images of the coupling devices at the otherend section, receiver means located at each end of said main conductorline, the coupling devices of both end sections having a pulse appliedat the first end of said first coupling segment so that the pulsecouples to said main line segment travelling from the second end to thefirst end along said main line Conductor receives at the other end ofsaid main line conductor, a further receiver means connected to saidmain line conductor between said first and second end sections, saidfurther receiver receiving pulses from the coupling devices of both endsections.